Coating composition for metal substrates

ABSTRACT

A coating composition for application to primed metal substrates as a topcoat is disclosed. The coating composition is especially useful on metal closures for vacuum-packed food products. The coating composition is free of a halide-containing vinyl polymer and comprises: (a) an acrylate copolymer having pendant glycidyl groups, (b) an acid-terminated polyester, and (c) a nonaqueous carrier.

FIELD OF THE INVENTION

[0001] The present invention relates to coating compositions for metalsubstrates, methods of coating a metal substrate, and metal articleshaving a coating composition applied thereon. The coating compositioncomprises: (a) an acrylate copolymer having pendant glycidyl groups and(b) an acid-terminated polyester in (c) a nonaqueous carrier, and isfree of a halide-containing vinyl polymer. The coating composition,after curing, is useful as a topcoat for the interior of metal closuresand demonstrates excellent flexibility and excellent adhesion to primercoats and to plastisol gaskets.

BACKGROUND OF THE INVENTION

[0002] It is well known that an aqueous solution in contact with anuntreated metal substrate can result in corrosion of the untreated metalsubstrate. Therefore, a metal article, such as a metal closure orcontainer for a water-based product, like a food or beverage, isrendered corrosion resistant in order to retard or eliminateinteractions between the water-based product and the metal article.Generally, corrosion resistance is imparted to the metal article, or toa metal substrate in general, by passivating the metal substrate or bycoating the metal substrate with a corrosion-inhibiting coating.

[0003] Investigators continually have sought improved coatingcompositions that reduce or eliminate corrosion of a metal article andthat do not adversely affect an aqueous product packaged in the metalarticle. For example, investigators have sought to improve theimperviousness of the coating in order to prevent corrosion-causingions, oxygen molecules, and water molecules from contacting andinteracting with a metal substrate. Imperviousness can be improved byproviding a thicker, more flexible, and more adhesive coating, but oftenimproving one particular advantageous property is achieved at theexpense of another advantageous property.

[0004] In addition, practical considerations limit the thickness,adhesive properties, and flexibility of a coating applied to a metalsubstrate. For example, thick coatings are expensive, require a longercure time, can be esthetically unpleasing, and can adversely affect theprocess of stamping and molding the coated metal substrate into a usefulmetal article. Similarly, the coating should be sufficiently flexiblesuch that the continuity of the coating is not destroyed during stampingand molding of the metal substrate into the desired shape of the metalarticle.

[0005] Investigators also have sought coatings that possess chemicalresistance in addition to corrosion inhibition. A useful coating for theinterior of a metal closure or container must be able to withstand thesolvating properties of the packaged product. If the coating does notpossess sufficient chemical resistance, components of the coating can beextracted into the packaged product and adversely affect the product.Even small amounts of extracted coating components can adversely affectsensitive products, such as beer, by imparting an off-taste to theproduct.

[0006] Organic solvent-based coating compositions provide cured coatingshaving excellent chemical resistance. Such solvent-based compositionsinclude ingredients that are inherently water insoluble, and, thereby,effectively resist the solvating properties of water-based productspackaged in the metal container.

[0007] Epoxy-based coatings and polyvinyl chloride-based coatings havebeen used to coat the interior of metal closures and containers forfoods and beverages because these coatings exhibit an acceptablecombination of adhesion, flexibility, chemical resistance, and corrosioninhibition. Polyvinyl chloride-based coatings and vinyl acetate/vinylchloride copolymer-based (i.e., solution vinyl) coatings also have beenthe topcoat of choice for the interior of metal closures because thesecoatings provide excellent adhesion to plastisol sealer gaskets appliedover the cured topcoat. However, epoxy-based coatings and polyvinylchloride-based coatings have serious disadvantages that investigatorsstill are attempting to overcome.

[0008] For example, polyvinyl chloride-based coating compositions arethermoplastic. Thermoplastic coatings used as the topcoat of theinterior coating of metal closures have inherent performancedisadvantages, such as potential softening during the closuremanufacturing process or under food processing conditions. Therefore,coating compositions having a thermosetting character have beeninvestigated.

[0009] In addition, coatings based on polyvinyl chloride or a relatedhalide-containing vinyl polymer, like polyvinylidene chloride, possessesthe above-listed advantageous properties of chemical resistance andcorrosion inhibition, and are economical. However, curing a polyvinylchloride or related halide-containing vinyl polymer can generate toxicmonomers, such as vinyl chloride, a known carcinogen. In addition, thedisposal of a halide-containing vinyl polymer, such as by incineration,also can generate toxic monomers. The generated vinyl chloride therebyposes a potential danger to workers in metal can and closuremanufacturing plants, in food process and packaging plants, and atdisposal sites. Disposal of polyvinyl chloride and related polymers alsocan produce carcinogenic dioxins and environmentally harmfulhydrochloric acid.

[0010] Government regulators are acting to eliminate the use ofpolyvinyl chloride-based coating compositions that contact food, andthereby eliminate the environmental and health concerns associated withhalide-containing vinyl polymers. Presently, however, polyvinylchloride-based compositions are still used to coat the interior of foodand beverage containers and closures.

[0011] To overcome the environmental concerns and performance problemsassociated with polyvinyl chloride-based coating compositions,epoxy-based coating compositions recently have been used to coat theinterior of food and beverage containers. However, epoxy-based coatingsalso possess disadvantages. For example, epoxy-based coatingcompositions are more expensive than polyvinyl chloride-based coatingcompositions.

[0012] In addition, epoxy-based coatings are prepared from monomers suchas bisphenol A and bisphenol A diglycidyl ether (BADGE), for example.

[0013] Epoxy resins have a serious disadvantage in that residual amountsof glycidyl ether and bisphenol monomers are present in the resin,typically in an amount of about 0.5% by weight. The presence of suchmonomers, and especially a glycidyl ether monomers, raises seriousenvironmental and toxicological concerns, especially because a glycidylether monomer can be extracted from a cured coating on the interior of ametal container by a product stored in the container. Accordingly,regulatory agencies have promulgated regulations reducing the amount ofa glycidyl ether monomer in coating compositions, and especially coatingcompositions used on the interior of food and beverage containers.

[0014] Coating compositions also typically include a phenolic resin.Phenolic resins prepared from bisphenol A or similar bisphenols also cancontain residual bisphenol monomers, similar to epoxy-based coatings.Phenolic resins also have disadvantages in that the resins can generateformaldehyde, which can adversely affect a product stored in a coatedmetal container. Accordingly, it would be an advance in the art toovercome the problems and disadvantages associated with coatingcompositions for metal substrates that contain an epoxy resin, ahalide-containing vinyl polymer, and/or a phenolic resin.

[0015] With respect to a metal closure for a food container, theinterior of a metal closure conventionally can be coated with threeseparate coating compositions, i.e., a three-coat system. First, anepoxy/phenolic primer is applied to the metallic substrate and cured,then a vinyl-based middle coat is applied over the cured primer.Finally, after curing the middle coat, a specially formulated topcoatcapable of adhering to a plastisol sealer is applied over the curedmiddle coat. The plastisol sealer is applied over the cured topcoat, andformed into a gasket during manufacture of a metal closure from a metalsheet having the three cured layers of coatings applied thereon.

[0016] Two-coat systems are the primary commercial system, but alsoexhibit disadvantages. Investigators are attempting to develop animproved two-coat system for coating the interior of a metal closure. Anideal two-coat system maintains corrosion inhibition, lowers the cost ofapplying the coatings, has improved rheological properties, has improvedcured film integrity, is free of a polyvinyl chloride-based resin,residual bisphenol monomers, and residual glycidyl ether monomers. Inaddition, it would be desirable to provide a top coat that acts as abarrier against the migration of bisphenol and glycidyl ether monomersfrom an epoxy resin-based primer coat.

[0017] A two-coat system for the interior of metal food closurecomprises a primer (i.e., a size) and a topcoat. The metal closurestypically are used in conjunction with a glass or plastic container. Thetopcoat must have sufficient adhesion to the primer or the coating willfail. In order to achieve sufficient intercoat adhesion, the chemicalmakeup of the topcoat often was dictated by the chemical makeup of theprimer. Investigators, therefore, have been seeking a more “universal”topcoat, i.e., a topcoat that can be applied to a variety of differentprimers and that exhibits sufficient intercoat adhesion. Such auniversal topcoat would be a significant advance in the art.

[0018] The coatings used on the interior of a metal food closure alsomust meet other criteria in addition to performance. For example, thecoatings must incorporate components acceptable to the U.S. Food andDrug Administration (FDA) because the cured coating composition contactsfood products.

[0019] The cured primer and topcoat, therefore, require sufficientadhesion to maintain film integrity during closure fabrication. Thecured primer and topcoat also require sufficient flexibility towithstand closure fabrication. Sufficient coating adhesion andflexibility also are needed for the closure to withstand processingconditions the closure is subject to during product packaging.

[0020] Other required performance features of the cured coatings includecorrosion protection and adequate adhesion to the plastisol gasketapplied over the cured topcoat. Also, the cured coating compositionrequires sufficient chemical resistance and sufficient abrasion and marresistance.

[0021] In the manufacture of a metal closure, a metal sheet is coatedwith the coating compositions, and each coating is cured individually,then the metal sheet is formed into the shape of a metal closure. Theclosures are made in a variety of sizes ranging from 27 mm (millimeter)to 110 mm in diameter. During manufacture, a plastisol material isapplied over the cured coatings on the interior of the metal closure.This plastisol subsequently is formed into a gasket and cured. Thegasket ensures an effective seal between the metal closure and glasscontainer, and to maintain the vacuum condition of the packaged foodproduct.

[0022] Product packaging is performed under processing conditionswherein the plastisol gasket is softened. When the metal closure ispressed onto the glass container, the threads on the glass containerform impressions in the softened plastisol gasket. The metal closure issecured in place both by the thread impressions and by the vacuumproduced by subsequent cooling. This type of metal closure is used forbaby food containers and for other packaged food and beverage products,such as juices and gravies. Other types of closures are designed to besecured to glass containers by lugs rather than by thread impressions inthe plastisol.

[0023] Vinyl chloride-based topcoat compositions have been softened bothby product processing conditions, and by conditions encountered duringclosure manufacture, thereby leading to closure failure. The presentinvention is directed, in part, to overcoming such closure failures.

[0024] Investigators, therefore, have sought a two-coat system for theinterior of metal closures used for vacuum-packed food products.Investigators have particularly sought a vinyl halide-free topcoat forthe interior of metal closures for food and beverages that retains theadvantageous properties of a vinyl chloride-based topcoat, such asadhesion, flexibility, chemical resistance, corrosion inhibition, andfavorable economics. Investigators especially have sought a coatingcomposition that demonstrates these advantageous properties and alsoreduces the environmental and toxicological concerns associated withhalide-containing vinyl polymers, formaldehyde, and residual glycidylether and bisphenol monomers.

[0025] Two-coat systems have been investigated and used for applicationto the interior of metal closures. Investigators sought and used topcoatcompositions having a sufficiently flexible cured coating such that acoated metal substrate can be deformed without destroying filmcontinuity. This is an important property because the metal substrate iscoated prior to deforming, i.e., shaping, the metal substrate into ametal article, like a metal closure. Coating a metal substrate prior toshaping the metal substrate is the present standard industrial practice.

[0026] A present topcoat coating composition includes: (a) an acrylatecopolymer having pendant glycidyl groups, typically a glycidyl(meth)acrylate-alkyl (meth)acrylic copolymer, and (b) an acid-terminatedpolyester, wherein the composition is free of a halide-containing vinylpolymer, and which, after curing, demonstrates: (1) excellentflexibility, (2) excellent adhesion to the primer coat, (3) excellentchemical resistance and corrosion inhibition, (4) excellent adhesion tothe plastisol gasket, and (5) reduced environmental and toxicologicalconcerns.

[0027] As an added advantage, a present topcoat coating composition isan improved two-coat system, thereby eliminating the presence of ahalide-containing vinyl polymer and the presence of residual bisphenoland glycidyl ether monomers, while providing an effective barrieragainst migration of residual bisphenol and glycidyl ether monomers fromthe size coat. The present topcoat coating composition also can be usedwith a variety of types of primers without a significant decrease incoating properties.

SUMMARY OF THE INVENTION

[0028] The present invention is directed to a coating composition that,after curing, effectively inhibits corrosion of metal substrates, isflexible, and exhibits excellent adhesion both to a primer coat and to avariety of plastisol gaskets used to ensure the vacuum seal of a metalclosure to a glass container. The present coating composition comprises:an acrylate copolymer having pendant glycidyl groups and anacid-terminated polyester in a nonaqueous carrier. The present coatingcomposition also is free of (a) a halide-containing vinyl polymer, suchas polyvinyl chloride, (b) formaldehyde, and (c) glycidyl ether andbisphenol monomers, such as BADGE and bisphenol A, used in thepreparation of an epoxy resin. Nevertheless, after curing andcrosslinking, the coating compositions demonstrate excellent adhesionboth to a primer coat and to a plastisol gasket.

[0029] The coating composition effectively inhibits corrosion of ferrousand nonferrous metal substrates when the composition is applied as atopcoat to a metal substrate, then cured for a sufficient time and at asufficient temperature to provide a crosslinked coating. A cured andcrosslinked coating demonstrates sufficient chemical and physicalproperties for use as the topcoat of a two-coat system on the interiorof metal closures used in packaging foods and beverages. The coatingcomposition does not adversely affect products packaged in a containerhaving a metal closure coated on the interior surface with the curedcomposition.

[0030] In particular, the present coating composition comprises: (a)about 50% to about 90%, by weight of nonvolatile material, of anacrylate copolymer having pendant glycidyl groups, for example, aglycidyl (meth)acrylate-alkyl (meth)acrylate copolymer and (b) about 10%to about 50%, by weight of nonvolatile material, of an acid-terminatedpolyester, wherein the composition is free of a halide-containing vinylpolymer. The weight ratio of glycidyl-containing monomers, e.g.,glycidyl methacrylate, to alkyl (meth)acrylate in the copolymer is about1:1 to about 1:20.

[0031] Components (a) and (b) are dispersed in a nonaqueous carrier suchthat the total coating composition includes about 20% to about 80%, byweight of the total composition, of components (a) and (b). Otheroptional components, such as a curing catalyst, a pigment, a filler, ora lubricant, also can be included in the composition, and, accordingly,increase the weight percent of total nonvolatile material in thecomposition to above about 80% by weight of the total coatingcomposition.

[0032] As used here and hereinafter, the term “coating composition” isdefined as the composition including the acrylate copolymer havingpendant glycidyl groups, alkyl (meth)acrylate copolymer, theacid-terminated polyester, and any optional ingredients dispersed in thenonaqueous carrier. The term “cured coating composition” is defined asthe adherent polymeric coating resulting from curing a coatingcomposition. The cured coating composition comprises the acrylatecopolymer having pendant glycidyl groups-alkyl (meth)acrylate copolymerand the acid-terminated polyester essentially in the amounts theseingredients are present in the coating composition, expressed asnonvolatile material.

[0033] Therefore, one important aspect of the present invention is toprovide a coating composition that enhances the ability of the primer toinhibit corrosion of ferrous and nonferrous metal substrates. Afterapplication to a primed metal substrate as a topcoat, and subsequentcuring at a sufficient temperature for a sufficient time, the coatingcomposition provides an adherent layer of a cured coating composition.The cured coating composition enhances corrosion inhibition, hasexcellent flexibility, and exhibits excellent adhesion both to a varietyof different of primer types applied to the metal substrate and to avariety of different types of plastisol sealer gaskets applied over thecured coating composition.

[0034] Because of these properties, an improved two-coat system isavailable for application to the metal substrate thereby providingeconomies in time, material, and machinery in the coating of a metalsubstrate. The coating composition also provides economies because thecomposition can be used with a variety of primers and plastisol gasketsof different chemical types. The closure manufacturer, therefore, canuse the coating composition in a more universal range of applications,thereby eliminating the need to stock an inventory of different topcoatsand eliminating application equipment changeover.

[0035] In accordance with another important aspect of the presentinvention, a cured coating composition demonstrates excellentflexibility and adhesion with respect to the plastisol sealer gasket.The excellent adhesion between the cured coating composition and theplastisol sealer gasket further improves the vacuum seal between a metalclosure and a glass container to maintain product integrity, and theexcellent flexibility facilitates processing of the coated metalsubstrate into a coated metal article, like in molding or stampingprocess steps, such that the cured coating remains in continuous andintimate contact with the primer on the metal substrate.

[0036] In accordance with yet another important aspect of the presentinvention, the cured coating composition demonstrates an excellentflexibility and adhesion even though the coating composition does notinclude a halide-containing vinyl polymer. Conventional coatingcompositions included a polyvinyl chloride to impart flexibility to thecured coating and to provide adhesion to the plastisol gasket. However,the presence of polyvinyl chloride adversely affected the heatresistance of the cured composition. A present coating composition,which excludes a halide-containing vinyl polymer (and glycidyl ether andbisphenol monomers), has excellent heat resistance, and, surprisingly,excellent flexibility.

[0037] In accordance with yet another important aspect of the presentinvention, a primed metal substrate coated on at least one surface witha cured coating composition of the present invention can be formed intoa metal closure for a glass or plastic container that holds foodproducts. Conventionally, a particular type of topcoat was applied overa particular primer in order to achieve sufficient intercoat adhesion.The present coating composition overcomes this disadvantage, andprovides a cured coating composition that exhibits sufficient intercoatadhesion with a variety of types of primers, and with a variety of typesof plastisol sealers.

[0038] These and other aspects and advantages of the present inventionwill become apparent from the following detailed description of thepreferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] A coating composition of the present invention, after curing,provides a cured coating composition that effectively enhances corrosioninhibition of primed metal substrates, such as, but not limited to,aluminum, iron, steel, and copper. A present coating composition, aftercuring, also demonstrates excellent adhesion to the primer coat appliedto the metal substrate and to a plastisol gasket, excellent chemical andscratch resistance, and excellent flexibility.

[0040] Accordingly, a coat between the primer and topcoat, i.e., themiddle coat, can be eliminated. The present coating compositions,therefore, are useful in an improved two-coat system comprising a primerand a topcoat. The present coating compositions are especially useful asthe topcoat of a two-coat system for the interior of a metal closure forvacuum-packed food products, because the topcoat is free of a vinylhalide-containing polymer, residual bisphenol monomers, and residualglycidyl ether monomers, and provides an effective barrier against themigration of residual bisphenol and glycidyl ether monomers from thesize coat.

[0041] A present coating composition comprises: (a) an acrylatecopolymer having pendant glycidyl groups, typically a glycidyl(meth)acrylate-alkyl (meth)acrylate copolymer, (b) an acid-terminatedpolyester, and (c) a nonaqueous carrier. A coating composition of thepresent invention is free of a halide-containing vinyl polymer,formaldehyde, and glycidyl ether and bisphenol monomers, like bisphenolA and BADGE. In addition, a present coating composition can includeoptional ingredients, like a catalyst or pigment, that improve theesthetics of the composition, that facilitate processing of thecomposition, or that improve a functional property of the composition.The individual composition ingredients are described in more detailbelow.

(a) Acrylate Copolymer Having Pendant Glycidyl Groups

[0042] The coating composition of the present invention comprises anacrylate copolymer having pendant glycidyl groups in an amount of about50% to about 90%, and preferably about 55% to about 80%, by weight ofnonvolatile material. To achieve the full advantage of the presentinvention, the coating composition comprises about 60% to about 70% ofthe acrylate copolymer, by weight of nonvolatile material.

[0043] An acrylate copolymer having pendant glycidyl groups that isuseful in the present invention contains about 5 to about 50 weight %,and preferably about 10 to about 40 weight %, of a monomer containing aglycidyl group, for example, glycidyl methacrylate. To achieve the fulladvantage of the present invention, the acrylate copolymer containsabout 15 to about 25 weight % of a monomer containing a glycidyl group.Similarly, the alkyl (meth)acrylate is present in the copolymer in anamount of about 50 to about 95 weight %, preferably about 60 to about 90weight %, and preferably about 75 to about 85 weight %. The copolymeralso can contain 0 to 10 weight %, and preferably 0 to 5 weight %, of anoptional monounsaturated monomer.

[0044] The monomer containing a glycidyl group can be any monomer havinga carbon-carbon double bond and a glycidyl group. Typically, the monomeris a glycidyl ester of an α, β-unsaturated acid, or anhydride thereof.The α, β-unsaturated acid can be a monocarboxylic acid or a dicarboxylicacid. Examples of such carboxylic acids include, but are not limited to,acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylic acid,α-cyanoacrylic acid, β-methylacrylic acid (crotonic acid),α-phenylacrylic acid, β-acryloxypropionic acid, sorbic acid,α-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid,β-stearylacrylic acid, itaconic acid, citraconic acid, mesaconic acid,glutaconic acid, aconitic acid, maleic acid, fumaric acid,tricarboxyethylene, maleic anhydride, and mixtures thereof. Specificexamples of monomers containing a glycidyl group are glycidyl(meth)acrylate (i.e., glycidyl methacrylate and glycidyl acrylate),mono- and di-glycidyl itaconate, mono- and di-glycidyl maleate, andmono- and di-glycidyl formate. It also is envisioned that allyl glycidylether and vinyl glycidyl ether can be used as the monomer.

[0045] It also should be pointed out that the acrylate copolymer caninitially be a copolymer of an α, β-unsaturated acid and an alkyl(meth)acrylate, which then is reacted with a glycidyl halide ortosylate, e.g., glycidyl chloride, to position pendant glycidyl groupson the acrylate copolymer. The α, β-unsaturated carboxylic acid can bean acid listed above, for example.

[0046] In an alternative embodiment, an acrylate copolymer havingpendant hydroxyl groups first is formed. The copolymer then is reactedto position pendant glycidyl groups on the acrylate polymer. Theacrylate copolymer having pendant hydroxyl groups can be prepared byincorporating a monomer like 2-hydroxyethyl methacrylate or3-hydroxypropyl methacrylate into the acrylate copolymer.

[0047] A preferred monomer containing a glycidyl group is glycidyl(meth)acrylate having the following structure:

[0048] wherein R¹ is hydrogen or methyl.

[0049] The monomer containing a glycidyl group, or the monomer thatcontains a group (like carboxyl or hydroxyl) that can be converted to aglycidyl group, is copolymerized with an alkyl (meth)acrylate having thestructure:

[0050] wherein R¹ is hydrogen or methyl, and R² is an alkyl groupcontaining one to sixteen carbon atoms.

[0051] The R² group can be substituted with one or more, and typicallyone to three, moieties such as hydroxy, halo, amino, phenyl, and alkoxy,for example. The alkyl (meth)acrylates used in the copolymer thereforeencompass hydroxy alkyl (meth)acrylates and aminoalkyl (meth)acrylates.The alkyl (meth)acrylate typically is an ester of acrylic or methacrylicacid. Preferably, R¹ is methyl and R² is an alkyl group having two toeight carbon atoms. Most preferably, R¹ is methyl and R² is an alkylgroup having two to four carbon atoms. Examples of the alkyl(meth)acrylate include, but are not limited to, methyl, ethyl, propyl,isopropyl, butyl, isobutyl, pentyl, isoamyl, hexyl, 2-aminoethyl,2-hydroxyethyl, 2-ethylhexyl, cyclohexyl, decyl, isodecyl, benzyl,2-hydroxypropyl, lauryl, isobornyl, octyl, and nonyl (meth)acrylates.

[0052] Optional monounsaturated monomers suitable for copolymerizingwith the monomer containing a glycidyl group (or monomer having a groupthat can be converted to a glycidyl group) and alkyl (meth)acrylateinclude, but are not limited to vinyl monomers, like styrene, ahalostyrene, isoprene, diallylphthalate, divinylbenzene, conjugatedbutadiene, α-methylstyrene, vinyl toluene, vinyl naphthalene, andmixtures thereof. Other suitable polymerizable vinyl monomers includeacrylonitrile, acrylamide, methacrylamide, methacrylonitrile, vinylacetate, vinyl propionate, vinyl butyrate, vinyl stearate,isobutoxymethyl acrylamide, and the like.

[0053] The glycidyl-containing monomer (or precursor thereof), alkyl(meth)acrylate, and optional monounsaturated monomers are polymerized bystandard free radical polymerization techniques, e.g., using initiatorssuch as peroxides or peroxy esters, to provide a copolymer having aweight average molecular weight (M_(w)) of about 4,000 to about 50,000,and preferably about 7,500 to about 40,000. To achieve the fulladvantage of the present invention, the copolymer has an M_(w) of about10,000 to about 30,000. In the preparation of the copolymer, a chaintransfer agent, such as isopropyl alcohol or n-dodecyl mercaptan, can beused to control the M_(w) of the polymer.

[0054] The following example illustrates a glycidyl (meth)acrylate-alkyl(meth)acrylate copolymer used in the present invention.

EXAMPLE 1 Glycidyl Methacrylate-Ethyl Methacrylate Copolymer

[0055] Diisobutyl ketone (123.9 lbs.) was added to a clean reactionvessel equipped with a reflux condenser and blanketed with nitrogen(N₂). The diisobutyl ketone was heated to 302° F. A monomer premixcontaining 396.5 lbs. of ethyl methacrylate, 99.1 lbs. of glycidylmethacrylate, and 19.8 lb. of di-t-butylperoxide was metered into thereactor over a 2.5 to 3 hour time period, while maintaining thetemperature of the reaction mixture at 298° F. to 302° F. and under alow to no reflux. After the entire monomer blend was added to thereactor, the reaction mixture was held at 302° F. to 306° F., for twohours, followed by cooling the reaction mixture to 248° F. Then, afteradding 188.3 lb. of ethylene glycol monobutyl ether (i.e., butylcellosolve) to the reaction mixture, the mixture was stirred for 30minutes. Then, 88.8 lb. of propylene glycol monomethyl ether was addedto the reaction mixture. The resulting reaction product contained 55% byweight of the glycidyl methacrylate-ethyl methacrylate copolymer. Thereaction product weighed about 8.37 lb./gal. The copolymer containedabout 79.5% ethyl methacrylate and 20.5% glycidyl methacrylate. Gasphase chromatography showed that the copolymer had an M_(w) of about19,250, and an M_(n) of about 4,900.

(b) Acid-Terminated Polyester

[0056] In addition to the glycidyl methacrylate-alkyl (meth)acrylatecopolymer, a present coating composition comprises a polyester to impartflexibility to the cured coating composition. The polyester is presentin the composition in an amount of about 10% to about 50%, andpreferably about 20% to about 45%, by weight of nonvolatile material. Toachieve the full advantage of the present invention, the polyester ispresent in an amount of about 30% to about 40%, by weight of nonvolatilematerial.

[0057] The polyester has a weight average molecular weight (M_(w)) ofabout 1,000 to about 50,000, and preferably about 5,000 to about 40,000.To achieve the full advantage of the present invention, the polyesterhas an M_(w) of about 10,000 to about 30,000.

[0058] The identity of the polyester is not especially limited. However,it is important that the polyester is terminated at each end withcarboxylic acid groups. The terminal carboxylic acid groups of thepolyester, therefore, are available to react with the oxirane ring ofthe pendant glycidyl groups of the copolymer, and thereby provide acrosslinked acrylate coating.

[0059] The polyesters are prepared from an aromatic or aliphaticpolycarboxylic acid and an aliphatic diol, triol, or polyol. Theseingredients are reacted to provide a polyester having terminalcarboxylic acid groups. Carboxylic acid groups can be positioned at theterminal end of the polyester by utilizing excess dicarboxylic acid inthe reaction. A triol or polyol is used to provide a branched, asopposed to linear, polyester. Accordingly, the acid-terminatedpolyesters have an acid number of about 20 to about 200 mg KOH/g, andpreferably about 40 to about 150 mg KOH/g. To achieve the full advantageof the present invention, the polyester has an acid number of 60 toabout 100 mg KOH/g. The polyester has a hydroxyl number of about 5 toabout 20 mg KOH/g.

[0060] Examples of diols, triols, and polyols include, but are notlimited to, ethylene glycol, propylene glycol, 1,3-propanediol,glycerol, diethylene glycol, dipropylene glycol, triethylene glycol,trimethylolpropane, trimethylolethane, tripropylene glycol, neopentylglycol, pentaerythritol, 1,4-butanediol, trimethylol propane, hexyleneglycol, cyclohexanedimethanol, a polyethylene or polypropylene glycolhaving an M_(w) of about 500 or less, isopropylidenebis(p-phenylene-oxypropanol-2), and mixtures thereof.

[0061] Examples of polycarboxylic acids or anhydrides include, but arenot limited to, maleic anhydride, maleic acid, fumaric acid, succinicanhydride, succinic acid, adipic acid, phthalic acid, phthalicanhydride, 5-tert-butyl isophthalic acid, tetrahydrophthalic anhydride,hexahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride,azelaic acid, sebacic acid, tetrachlorophthalic anhydride, chlorendicacid, isophthalic acid, trimellitic anhydride, terephthalic acid, anaphthalene dicarboxylic acid, cyclohexane-dicarboxylic acid, glutaricacid, and mixtures thereof. It is also understood that an esterifiablederivative of a polycarboxylic acid, such as a dimethyl ester oranhydride of a polycarboxylic acid, can be used to prepare thepolyester.

[0062] A typical polyester is illustrated in Example 2. The diol, triol,and polycarboxylic acid and anhydride, in correct proportions, arereacted using standard esterification procedures to provide a polyesterhaving carboxylic acid functionalities at the terminal ends of thepolyester.

[0063] The following example illustrates an acid-terminated polyesterused in the present invention.

EXAMPLE 2 Acid-Terminated Polyester

[0064] Neopentyl glycol (125.2 lb.), ethylene glycol (43.1 lb.),trimethylolpropane (21.7 lb.), and isophthalic acid (166.7 lb.) werecharged into a reaction vessel as the reaction vessel was heated to 150°F. under a nitrogen (N₂) blanket. After the reactants were introducedinto the reaction vessel, the reaction mixture was heated until theonset of water distillation. Heating was continued to maintain theoverhead column temperature at less than 205° F. The refractive index ofthe distillate was monitored to remain at 1.337 or below. If therefractive index increased above 1.337, additional ethylene glycol wasadded to the reaction mixture to adjust the refractive index to 1.337 orbelow. Heating was continued until the reaction mixture reached 460° F.,then the reaction mixture was held at 450° F. until the acid number wasbelow 8 mg KOH/g. The reaction mixture was cooled to between 350° F. to365° F., followed by the addition of 62.2 lbs. of trimellitic anhydride.The temperature of the resulting reaction mixture was raised to 435° F.to 438° F. and held for 15 minutes. The acid number of the reactionmixture then was about 70 to about 80 mg KOH/g. The reaction mixturethen was cooled to 284° F., followed by the addition of 319.8 lb. ofaromatic solvent and 80 lbs. of propylene glycol monomethyl ether. Theresulting acid-terminated polyester solution contained 55% by weightnonvolatile matter, and had a weight/gallon of 9.10 lbs./gal. Theacid-terminated polyester had a Tg (glass transition temperature) of 2°C., as determined by Differential Scanning Calorimetry (DSC), and anM_(w) of about 10,800.

[0065] Four other acid-terminated polyesters were prepared by the methodset forth in Example 2. These polyesters had an M_(w) of 11,600, 15,800,6,100, and 25,600, respectively, and a Tg of 15° C., 75° C., 3° C., and11° C., respectively.

(c) Nonaqueous Carrier

[0066] A present coating composition is a nonaqueous composition,wherein the glycidyl methacrylate-alkyl (meth)acrylate copolymer and theacid-terminated polyester are homogeneously dispersed in a nonaqueouscarrier. It should be understood that the present coating compositioncan include a relatively low amount of water, such as up to about 5% bytotal weight of the composition, without adversely affecting thecorrosion-inhibiting coating composition, either prior to or aftercuring. The water can be added to the composition intentionally, or canbe present in the composition inadvertently, such as when water ispresent in a particular component included in the coating composition.

[0067] In general, the nonaqueous carrier has sufficient volatility toevaporate essentially entirely from the coating composition during thecuring process, such as during heating at about 350° F. to about 400° F.for about 8 to about 12 minutes. Suitable nonaqueous carriers are knownin the art of coating compositions, and include, for example, but arenot limited to, glycol ethers, like ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, andpropylene glycol monomethyl ether; ketones, like cyclohexanone, ethylaryl ketones, methyl aryl ketones, and methyl isoamyl ketone; aromatichydrocarbons, like toluene, benzene, and xylene; aliphatic hydrocarbons,like mineral spirits, kerosene, and high flash VM&P naphtha; alcohols,like isopropyl alcohol, n-butyl alcohol, and ethyl alcohol; and aproticsolvents, like tetrahydrofuran; chlorinated solvents; esters; glycolether esters, like propylene glycol monomethyl ether acetate; andmixtures thereof.

[0068] The nonaqueous carrier usually is included in the composition ina sufficient amount to provide a composition including about 20% toabout 80% of (a) and (b), by total weight of the composition. The amountof nonaqueous carrier included in the composition is limited only by thedesired, or necessary, rheological properties of the composition.Usually, a sufficient amount of nonaqueous carrier is included in thecoating composition to provide a composition that can be processedeasily and that can be applied to a metal substrate easily anduniformly, and that is sufficiently removed from the coating compositionduring curing within the desired cure time.

[0069] Therefore, essentially any nonaqueous carrier is useful in thepresent coating composition as long as the nonaqueous carrier adequatelydisperses and/or solubilizes the composition components, is inert withrespect to interacting with composition components, does not adverselyaffect the stability of the coating composition or the ability of thecorrosion-inhibition coating to inhibit corrosion of a metal substrate,and evaporates quickly, essentially entirely, and relatively rapidly toprovide a cured coating composition that inhibits the corrosion of ametal substrate, demonstrates good adhesion and flexibility, and hasgood chemical and physical properties.

(d) Other Optional Ingredients

[0070] A coating composition of the present invention also can includeother optional ingredients that do not adversely affect the coatingcomposition or a cured coating composition resulting therefrom. Suchoptional ingredients are known in the art, and are included in a coatingcomposition to enhance composition esthetics, to facilitatemanufacturing, processing, handling, and application of the composition,and to further improve a particular functional property of a coatingcomposition or a cured coating composition resulting therefrom.

[0071] Such optional ingredients include, for example, catalysts, dyes,pigments, toners, extenders, fillers, lubricants, anticorrosion agents,flow control agents, thixotropic agents, dispersing agents,antioxidants, adhesion promoters, light stabilizers, and mixturesthereof. Each optional ingredient is included in a sufficient amount toserve its intended purpose, but not in such an amount to adverselyaffect a coating composition or a cured coating composition resultingtherefrom.

[0072] One optional ingredient is a catalyst to increase the rate ofcure. The catalyst is present in an amount of 0% to about 1%, andpreferably about 0.05% to about 1%, by weight of nonvolatile material.Examples of catalysts, include, but are not limited to, quaternaryammonium compounds, phosphorous compounds, and tin and zinc compounds,like a tetraalkyl ammonium halide, a tetraalkyl or tetraaryl phosphoniumiodide or acetate, tin octoate, zinc octoate, triphenylphosphine, andsimilar catalysts known to persons skilled in the art.

[0073] Another useful optional ingredient is a lubricant, like a wax,which facilitates manufacture of metal closures by imparting lubricityto sheets of coated metal substrate. A lubricant is present in thecoating composition in an amount of 0% to about 2%, and preferably about0.1% to about 2%, by weight of nonvolatile material.

[0074] Another useful optional ingredient is a pigment, like titaniumdioxide or a toning phenolic resin. A pigment, like titanium dioxide, ispresent in the coating composition in an amount of 0% to about 50%, andpreferably about 10% to about 50%, by weight of nonvolatile material. Apigment, like a toning phenolic resin, is present in an amount of 0% toabout 20%, and preferably about 1% to about 10%, by weight ofnonvolatile material.

[0075] In accordance with an important feature of the present invention,the present coating composition is free of a halide-containing vinylpolymer, such as polyvinyl chloride. The phrase “free of ahalide-containing vinyl polymer” is defined as 1.5% or less of ahalide-containing vinyl polymer, by weight of nonvolatile material, asdiscussed hereafter.

[0076] Conventionally, a polyvinyl chloride was included in the coatingcomposition to improve composition economics and to improve adhesion ofa plastisol gasket material to the cured coating composition. However, ahalide-containing vinyl polymer adversely affects the heat resistance ofthe cured coating composition.

[0077] The present composition does not include a halide-containingvinyl polymer, yet has sufficient adhesion to a plastisol gasket toavoid failure of a metal closure for food products. In addition, thepresent composition exhibits an excellent heat resistance.

[0078] In accordance with an important feature of the present invention,a halide-containing vinyl polymer is not intentionally added to thecoating composition. However, 1.5% or less of halide-containing vinylpolymer, i.e., up to about 1.5%, by weight of nonvolatile material, maybe present in the coating composition as an inadvertent ingredient. Forexample, various resins are dust-coated with a halide-containing vinylpolymer as an additive. Incorporating a dust-coated resin into a presentcoating composition could introduce a halide-containing vinyl polymerinto the composition in an amount of up to 1.5% by weight of nonvolatilematerial. This amount of a halide-containing vinyl polymer does notadversely affect the cured coating composition.

[0079] A present coating composition also is free of phenolic resins andepoxy resins. Accordingly, the composition is free of formaldehyde, andof monomers used in the manufacture of epoxy resin, e.g., bisphenols,like bisphenol A, and glycidyl ether monomers, like BADGE. A presentcomposition, therefore, avoids the environmental and toxicologicalproblems associated with such compounds.

[0080] A coating composition of the present invention is prepared bysimply admixing the copolymer, the polyester, and any optionalingredients, in any desired order, in the nonaqueous carrier, withsufficient agitation. The resulting mixture is admixed until all thecomposition ingredients are homogeneously dispersed throughout thenonaqueous carrier. Then, an additional amount of the nonaqueous carriercan be added to the coating composition to adjust the amount ofnonvolatile material in the coating composition to a predeterminedlevel.

[0081] To demonstrate the usefulness of a coating composition of thepresent invention, the following examples were prepared, then applied toa metal substrate as a topcoat, and finally cured to provide a coatedmetal substrate. The coated metal substrates then were tested,comparatively, for use as a closure for a food or beverage container.The cured coatings were tested for an ability to inhibit corrosion of ametal substrate, for adhesion to the metal substrate and to a plastisolgasket, for chemical resistance, for flexibility, and for scratch andmar resistance.

[0082] The following Example 3 illustrates one embodiment of acomposition of the present invention and its method of manufacture.

EXAMPLE 3

[0083] Weight % (by weight % (by weight Amount of the total ofnonvolatile Ingredient (lbs.) composition) material) Butyl Cellosolve225.18 27.27% — Acrylate Copolymer¹⁾ 420.34 50.91% 70% Polyester²⁾180.14 21.82% 30%

[0084] The composition of Example 3 was prepared by adding the acryliccopolymer and the polyester to the butyl cellosolve portion of thesolvent, stirring until homogeneous, then adding the remainder of thesolvent. The resulting coating composition contained 40% by weightnonvolatile material and weighed 8.26 lb./gal. The makeup of the 60% byweight of solvents is 7.0% propylene glycol monomethyl ether, 38.0%ethylene glycol monobutyl ether (i.e., butyl cellosolve), 7.9% aromaticsolvent, and 7.1% diisobutyl ketone. The coating composition of Example3 was applied as a topcoat to a metal substrate over a primer, thencured for a sufficient time at a sufficient temperature, such as forabout 8 to about 12 minutes at about 350° F. to about 400° F., toprovide an adherent, crosslinked, cured coating composition on the metalsubstrate.

[0085] A major function of the cured coating composition of Example 3 isto provide a coating layer that: (1) enhances corrosion inhibition ofthe metal substrate, and (2) provides a coating capable of adhering tothe plastisol gasket. The composition of Example 3 provides a barrieragainst migration of monomers like bisphenol A and BADGE, orformaldehyde, or vinyl polymers when applied over conventionalepoxy/phenolic primer coatings.

[0086] Conventionally, the primer provides sufficientcorrosion-inhibiting properties to adequately protect the metalsubstrate. However, corrosion inhibition occasionally was insufficientwhen only one topcoat was applied over the cured primer. Therefore, twotopcoats often were used (i.e., a three-coat system). Primers also donot have sufficient adhesion to a plastisol gasket to secure the gasketin place during closure manufacture or food processing.

[0087] A coating composition of the present invention, after curing,exhibits excellent chemical and physical properties, exhibits sufficientadhesion to the primer coat to obviate the second topcoat for all exceptthe very aggressive foods packaged in a container, and enhancescorrosion inhibition provided by the primer. The present compositionalso provides excellent adhesion to the plastisol gasket. In addition,the cured coating composition provided by a coating composition of thepresent invention is sufficiently adhesive to a variety of differenttypes of primer coats and plastisol gaskets, such that the coatingcomposition can be used in a more universal range of applications.

[0088] The coating composition of Example 3 also provided a curedcoating composition that exhibited excellent flexibility. Flexibility isan important property of a cured coating composition because the metalsubstrate is coated with a primer and topcoat prior to stamping orotherwise shaping the metal substrate into a desired metal article, suchas a metal container or a metal closure for bottles. The plastisolgasket, if present, is applied over the topcoat during the stampingprocess.

[0089] The coated metal substrate undergoes severe deformations duringthe shaping process, and if a cured coating composition lacks sufficientflexibility, the coating can form cracks, or fractures. Such cracksresult in corrosion of the metal substrate because the aqueous contentsof the container or bottle have greater access to the metal substrate.In addition, a cured coating composition provided by a composition ofthe present invention is sufficiently adhered to the primer duringprocessing into a metal article, thereby further enhancing corrosioninhibition.

[0090] The above-described advantages make a coating composition of thepresent invention useful for application on the interior surface of avariety of metal articles, such as for the interior of vacuum-packedmetal containers. The present coating composition is especially useful,after curing, as a corrosion-inhibiting coating on a metal closure forglass or plastic containers that hold food products, like baby food, orfood products including volatile acids, like relishes, pickles, and hotpeppers.

[0091] The compositions of the following Examples 4 through 8 wereprepared by the general method outlined above in Example 3. Thecompositions of Examples 4 through 8 then were applied to a metalsubstrate as a topcoat over a primer, and cured. The resulting coatingswere tested for a variety of properties, and compared to a controlcomposition.

[0092] The composition of Examples 4-8 were applied to electrolytic tinplate panels in a sufficient amount to provide 15 mg (milligrams) ofcured coating composition per 4 sq. in. (square inches) of panelsurface. The compositions of Examples 4-8 were applied over a commercialepoxy-phenolic primer coat. After application to the metal panel, thecomposition of Examples 4-8 were cured for 8 minutes at 370° F. Thecompositions of Examples 4-8 were compared to a commercial topcoatcomposition used on the interior of metal closure, i.e., a polyvinylchloride-based composition, which also contains a phenolic resin and apigment. The control composition was applied at a rate of 35 mg per 4sq. in. of the panel. Exhibit Exhibit Exhibit Exhibit Exhibit 4 5 6 7 8Glycidyl methacrylate- 37.5%¹⁾ 35.0% 32.5% 30.0% 25.0% ethylmethacrylate copolymer Acid-terminated 12.5% 15.0% 17.5% 20.05% 25.0% %Nonvolatile material 50% 50% 50% 50% 50% Copolymer/Polyester 75/25 70/3065/35 60/40 50/50 ratio

[0093] After curing the coating compositions, the panels coated witheither the compositions of Examples 4-8 or the control composition werefabricated into metal closures. Tests showed that the compositions ofExamples 4-8 passed fabrication of the closures, integrity requirementsat elevated temperatures, and compound adhesion tests.

[0094] Neither the control nor Examples 4-8 exhibited adhesion failure.In addition, none of the examples exhibited blocking failure. The curedcoatings also were subjected to methyl ethyl ketone (MEK) rubs. The MEKrub test measures resistance of a cured coating to chemical attack. Inthe MEK rub test, cheesecloth saturated with MEK is rubbed back andforth against a coated panel using hand pressure. A rub back and forthis designated as one “double rub.” In this test, the cured coating isrubbed until the MEK dissolves or otherwise disrupts the cured coating.A cured coating is less susceptible to chemical attack as the number ofMEK double rubs increases. The cured coating of Examples 4-8 required 35to 48 double rubs before the topcoat was broken through. In contrast,the cured control composition broke through after only seven double MEKrubs, even through the control composition was applied at greater thantwice the amount of Examples 4-8. These results show that a curedcoating composition of the present invention has excellent resistance tochemical attack compared to the control composition, and can be used asthe coating for the interior surface of a food or beverage container.

[0095] Closures having Examples 4-8 and the control composition as thetopcoat were subjected to an accelerated corrosion test by contact witha 5% by weight acetic acid solution for 30 days and 60 days at 100° F.The results are tabulated below: Pitting After Pitting After 30 Days(Avg.) 60 Days (Avg.) Control 1.7 20.7¹⁾ Example 4 3 4.3 Example 5 3.715 Example 6 7.7 11 Example 7 6.7 10.7 Example 8 10.7 12.7

[0096] The data summarized above shows that the coating compositions ofthe present invention out-performed the control composition. Inaddition, only minor differences in performance were observed by varyingthe ratio of acrylic copolymer to acid-terminated polyester.

[0097] This accelerated corrosion test was repeated using Example 3 at arate of 15 and 25 mg/4 sq. in. and cured for 8 minutes at 350° F. and370° F. The results are summarized below: Film Weight 30-day 60-day CureTemp. (mg/4 sq. in.) Test¹⁾ Test 370 15 10.5 33 350 15 9 10.8 370 25 0.519.5 350 25 4.8 25.8

[0098] The results show that Example 3 performed well as a topcoat for aclosure.

[0099] The composition of Example 3 was applied to electrolytic tinplate and tin-free steel at a rate of 15 mg/4 sq. in. and cured at 370°F. for 8 minutes. The coated metal then was formed into 51 mm and 63 mmclosures. The closures then were subjected to a variety of tests todetermine the suitability of the coating composition as a topcoat for aclosure. The closures were rated on a subjective scale of 0 (best) to 10(worst). A closure passes a particular test if the rating is 5 or less.A rating of 2 is equal to a rating for the control composition. In someinstances, the tests are rated with respect to degree of failure.

[0100] In particular, various products were packaged in a glasscontainer at 180° F. and immediately sealed with a metal closure. Thesealed containers were exposed to food processing conditions, likepasteurization for 30 minutes at 180° F. The containers then were cooledand examined for integrity. The containers also were tested for adhesionof the gasket to the coating.

[0101] The present coating compositions passed the cross hatch adhesiontest, acetic acid tests, sulfur dioxide tests, cystiene hydrochloridetests, and empty container and water-filled adhesion tests.

[0102] The properties demonstrated by a coating composition of thepresent invention, and a cured coating composition resulting therefrom,show that a halide-containing vinyl polymer is not necessary to provideadhesion to a primer coat or a plastisol gasket. The present coatingalso acts as an effective barrier against migration of formaldehyde,glycidyl ether monomers, and bisphenol monomers from the interior sizecoat of the closure. The present coating composition, therefore, isuseful as a topcoat on the interior of metal closures, and especiallymetal closures for food and beverage containers. The elimination of thehalide-containing vinyl polymer is important with respect to eliminatingthe environmental and toxicological concerns associated with suchpolymers. Surprisingly, the halide-containing vinyl polymer has beeneliminated, and the present composition maintains the advantageousphysical and chemical properties associated with compositions includinga halide-containing vinyl polymer. The present compositions alsoovercome the environmental and toxicological problems associated withprior epoxy-phenolic-based coatings by eliminating formaldehyde,glycidyl ether monomers, and bisphenol monomers from the composition,and by providing an effective barrier against migration of such monomersfrom the interior size coat.

[0103] The present coating composition can be used in conjunction with avariety of types of primers and plastisol gaskets. The present coatingcomposition, therefore, has a more universal range of applications. Thepresent coating compositions, unlike prior compositions, do not requirea pigment, like TiO₂, to achieve sufficient performance and filmintegrity. The performance characteristics of the present coatingcomposition is achieved by a novel combination of ingredients, asopposed to halide-containing vinyl polymers and pigments. The curedcoating composition also has a high gloss and tooling wear is reducedduring manufacture of the metal closure. These and the above-describedadvantages make a coating composition of the present inventionespecially useful for application on the interior surface of a metalclosure for food and beverage containers.

[0104] Obviously, many modifications and variations of the invention ashereinbefore set forth can be made without departing from the spirit andscope thereof, and, therefore, only such limitations should be imposedas are indicated by the appended claims.

What is claimed is:
 1. A coating composition for application to a primedmetal substrate comprising: (a) about 50% to about 90%, by weight ofnonvolatile material, of an acrylate copolymer having pendant glycidylgroups; (b) about 10% to about 50%, by weight of nonvolatile material,of an acid-terminated polyester; and (c) a nonaqueous carrier.
 2. Thecoating composition of claim 1 wherein the composition is free of ahalide-containing vinyl polymer.
 3. The composition of claim 1 whereinthe acrylate copolymer comprises (a) a monomer containing a glycidylgroup and (b) an alkyl (meth)acrylate.
 4. The composition of claim 3wherein the weight ratio of monomer containing a glycidyl group to alkyl(meth)acrylate in the copolymer is about 1:20 to about 1:1.
 5. Thecomposition of claim 1 wherein the acrylate copolymer is prepared bycopolymerizing a monomer containing a glycidyl group and analkyl-(methacrylate).
 6. The composition of claim 1 wherein the acrylatecopolymer is prepared by copolymerizing a monomer containing a moietycapable of conversion to a glycidyl group and an alkyl (meth)acrylate,followed by conversion of the moiety to a glycidyl group.
 7. Thecomposition of claim 5 wherein the monomer containing a glycidyl groupcomprises allyl glycidyl ether, vinyl glycidyl ether, or a glycidylester of an α, β-unsaturated carboxylic acid selected from the groupconsisting of acrylic acid, methacrylic acid, ethacrylic acid,α-chloroacrylic acid, α-cyanoacrylic acid, β-methylacrylic acid(crotonic acid), α-phenylacrylic acid, β-acryloxypropionic acid, sorbicacid, α-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamicacid, β-stearylacrylic acid, itaconic acid, citraconic acid, mesaconicacid, glutaconic acid, aconitic acid, maleic acid, fumaric acid,tricarboxyethylene, maleic anhydride, and mixtures thereof.
 8. Thecomposition of claim 6 wherein the monomer containing a moiety capableof conversion to a glycidyl group is selected from the group consistingof acrylic acid, methacrylic acid, ethacrylic acid, α-chloroacrylicacid, α-cyanoacrylic acid, β-methylacrylic acid (crotonic acid),α-phenylacrylic acid, β-acryloxypropionic acid, sorbic acid,α-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid,β-stearylacrylic acid, itaconic acid, citraconic acid, mesaconic acid,glutaconic acid, aconitic acid, maleic acid, fumaric acid,tricarboxyethylene, maleic anhydride, 2-hydroxyethyl methacrylate,3-hydroxypropyl methacrylate, and mixtures thereof.
 9. The compositionof claim 1 containing about 20% to about 80%, by total weight of thecomposition, of (a) and (b).
 10. The coating composition of claim 1further comprising 0% to about 2%, by weight of nonvolatile material, ofa lubricant, and 0% to about 50%, by weight of nonvolatile material, ofa pigment.
 11. The coating composition of claim 1 further comprising 0%to about 1%, by weight of nonvolatile material, of a catalyst.
 12. Thecoating composition of claim 11 wherein the catalyst is selected fromthe group consisting of a tetraalkyl ammonium halide, a tetraalkylphosphonium halide, a tetraalkyl phosphonium acetate, a tetraarylphosphonium halide, a tetraaryl phosphonium acetate, tin octoate, zincoctoate, a triaryl phosphine, and mixtures thereof.
 13. The coatingcomposition of claim 1 comprising about 55% to about 80%, by weight ofnonvolatile material, of the acrylate copolymer.
 14. The composition ofclaim 1 wherein the acrylate copolymer has a weight average molecularweight of about 4,000 to about 50,000.
 15. The composition of claim 3wherein the acrylate copolymer comprises about 10% to about 40% of amonomer having a pendant glycidyl group and about 60% to about 90% of analkyl (meth)acrylate.
 16. The composition of claim 15 wherein theacrylate copolymer further comprises 0% to about 10% of amonounsaturated monomer.
 17. The composition of claim 16 wherein themonounsaturated monomer is selected from the group consisting of a vinylmonomer, styrene, a halostyrene, isoprene, diallyl phthalate,divinylbenzene, conjugated butadiene, α-methylstyrene, vinyl toluene,vinyl naphthalene, acrylonitrile, acrylamide, methacrylamide,methacrylonitrile, vinyl acetate, vinyl propionate, vinyl butyrate,vinyl stearate, isobutoxymethyl acrylamide, and mixtures thereof. 18.The composition of claim 1 wherein the alkyl (meth)acrylate has aformula

wherein R¹ is hydrogen or methyl, and R² is an alkyl group having one tosixteen carbon atoms.
 19. The composition of claim 18 wherein R² isselected from the group consisting of methyl, ethyl, propyl, isopropyl,butyl, isobutyl, pentyl, isoamyl, hexyl, 2-aminoethyl, 2-hydroxyethyl,2-ethylhexyl, cyclohexyl, decyl, isodecyl, benzyl, 2-hydroxypropyl,lauryl, isobornyl, octyl, and nonyl.
 20. The composition of claim 18wherein the alkyl (meth)acrylate is ethyl (meth)acrylate.
 21. Thecomposition of claim 1 comprising about 20% to about 45%, by weight ofnonvolatile material, of the acid-terminated polyester.
 22. Thecomposition of claim 1 wherein the acid-terminated polyester has amolecular weight of about 1,000 to about 50,000.
 23. The composition ofclaim 1 wherein the polyester has a molecular weight of about 5,000 toabout 40,000.
 24. The composition of claim 1 wherein the acid-terminatedpolyester has an acid number of about 20 to about 200 mg KOH/g ofpolyester.
 25. The composition of claim 1 wherein the acid-terminatedpolyester is prepared from a diol or triol selected from the groupconsisting of ethylene glycol, propylene glycol, 1,3-propanediol,glycerol, diethylene glycol, dipropylene glycol, triethylene glycol,trimethylolpropane, trimethylolethane, tripropylene glycol, neopentylglycol, pentaerythritol, 1,4-butanediol, trimethylol propane, hexyleneglycol, cyclohexanedimethanol, a polyethylene or polypropylene glycolhaving an M_(w) of about 500 or less, isopropylidenebis(p-phenyleneoxypropanol-2), and mixtures thereof.
 26. The compositionof claim 1 wherein the acid-terminated polyester is prepared from apolycarboxylic acid or anhydride selected from the group consisting ofmaleic anhydride, maleic acid, fumaric acid, succinic anhydride,succinic acid, adipic acid, phthalic acid, phthalic anhydride,5-tert-butyl isophthalic acid, tetrahydrophthalic anhydride,hexahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride,azelaic acid, sebacic acid, tetrachlorophthalic anhydride, chlorendicacid, isophthalic acid, trimellitic anhydride, terephthalic acid, anaphthalene dicarboxylic acid, cyclohexanedicarboxylic acid, glutaricacid, and mixtures thereof.
 27. The composition of claim 1 wherein theacid-terminated polyester comprises a diol or triol selected from thegroup consisting of ethylene glycol, trimethylolpropane, neopentylglycol, and mixtures thereof, and a polycarboxylic acid selected fromthe group consisting of isophthalic acid, trimellitic anhydride, and amixture thereof.
 28. The composition of claim 1 wherein the compositionincludes up to about 1.5%, by weight of nonvolatile material, of ahalide-containing vinyl polymer.
 29. The composition of claim 5 whereinthe composition includes about 10% to about 50%, by weight ofnonvolatile material, of a pigment.
 30. The composition of claim 5wherein the pigment is titanium dioxide.
 31. The composition of claim 1comprising: (a) about 60% to about 70%, by weight of nonvolatilematerial, of a glycidyl (meth)acrylate-alkyl (meth)acrylate copolymercontaining about 15% to about 25% by weight glycidyl methacrylate; (b)about 30% to about 40%, by weight of nonvolatile material, of anacid-terminated polyester having a weight average molecular weight ofabout 10,000 to about 30,000; wherein the composition is free of ahalide-containing vinyl polymer.
 32. The composition of claim 31 furthercomprising about 0% to about 2% of a lubricant, about 10% to about 50%of a pigment, and 0% to about 1% of a catalyst, by weight of nonvolatilematerial.
 33. A method of coating a metal substrate comprising: (a)applying a primer coating composition to at least one surface of themetal substrate; (b) heating the metal substrate having the primercoating composition applied thereon for a sufficient time and at asufficient temperature to cure the primer coating composition andprovide a primed metal substrate; (c) applying a coating composition tothe primed metal substrate, said coating composition comprising: (i)about 50% to about 90%, by weight of nonvolatile material, of anacrylate copolymer having pendant glycidyl groups; (ii) about 10% toabout 50%, by weight of nonvolatile material, an acid-terminatedpolyester; and (iii) a nonaqueous carrier; and (d) heating the primedmetal substrate having the coating composition applied thereon for asufficient time and at a sufficient temperature to remove the nonaqueouscarrier from the composition and provide a crosslinked cured coatingcomposition.
 34. The method of claim 33 wherein the composition is freeof a halide-containing vinyl polymer.
 35. The method of claim 33 furthercomprising 0% to about 2% of a lubricant, 0% to about 50% of a pigment,and 0% to about 1% of a catalyst, each by weight of nonvolatilematerial.
 36. The method of claim 33 wherein the primed metal substratehaving the coating composition applied thereon is heated for about 8minutes to about 12 minutes at a temperature of about 350° F. to about400° F.
 37. A metal article having at least one surface thereof coatedwith a primer and an adherent layer of a cured coating composition, saidcured coating composition resulting from curing a coating compositioncomprising: (a) about 50% to about 90%, by weight of nonvolatilematerial, of a an acrylate copolymer having pendant glycidyl groups; (b)about 10% to about 50%, by weight of nonvolatile material, anacid-terminated polyester; and (c) a nonaqueous carrier.
 38. The metalarticle of claim 37 wherein the composition is free of ahalide-containing vinyl polymer.
 39. The metal article of claim 37further comprising 0% to about 2% of a lubricant, 0% to about 50% of apigment, and 0% to about 1% of a catalyst, each by weight of nonvolatilematerial.